This invention relates to a method of coating an article as it is produced during injection moulding and to the products of such a method. In particular, it relates to the use of paint for such coating.
Assembly industries are making increasing use of components produced by injection moulding. Frequently such components need to be coated in order to provide an article with the necessary surface finish; for example, painting body components of motor vehicles. Such industries have typically used painting shops. However, paint shops have a high capital cost and often require a long commissioning period before painted surfaces of sufficiently high quality can be achieved. In addition, they are environmentally unfriendly; provide an opportunity for foreign particles to accumulate on components awaiting painting; and represent an undesirable secondary operation.
In order to overcome these drawbacks attempts have been made to apply paint during the actual injection moulding step. Thus, a method of forming a moulding with a coating using dual injection is known. Typically, a plastics paint material is first injected into a mould so as to only partially fill the mould. A plastics substrate material is then injected within this plastics paint material so that as the moulding is formed the plastics paint material encapsulates the plastics substrate until at the end of the moulding process it forms an outer coating for the moulded article. While this method has many advantages over traditional secondary painting in spraying shops, there is one drawback; disruption of the paint flow due to a hole or other surface feature may result in so called “weld lines” in the vicinity of such features. This problem is particularly evident when metallic paints are used.
Powder paints and gel coats have been used to coat mould tools; but the tool has always been in the open condition. Even with careful masking of areas, paint generally coats the tool “shut-off” edge adversely affecting sealing.